1. Field of the Invention
The present invention relates to magnetic-tape recording apparatuses, magnetic-tape recording methods, magnetic tapes, and recording media, and more particularly, to a magnetic-tape recording apparatus, a magnetic-tape recording method, a magnetic tape, and a recording medium which (without fail) certainly capture data in variable-speed reading and which record data for displaying acceptable images.
2. Description of the Related Art
Technologies for compressing and recording image data and audio data have been advancing these days. As a low-bit-rate coding method, an Moving Picture Expert Group (MPEG) method is, for example, used.
When image data to which interframe compression has been applied by a low-bit-rate encoding method, such as MPEG2, and which is recorded into a recording medium by a rotating drum is read, if an attempt is made to read at a variable speed, two times or more faster in the positive direction or the normal speed or faster in the reverse direction, since obtained data has no relationship with each other (decoding cannot be performed with obtained data only), such reading at the variable speed cannot be achieved.
There has been proposed a method for allowing variable-speed reading, in which a reading speed is assumed in advance when compressed image data is recorded into a recording medium, and data to be read is recorded at a position where a head traces at the reading speed, separately from image data used for reading at a normal speed.
When the above proposed method is used, the following problems occur. Since the contact (touching) between a rotating head and the recording medium is designed so as to be most appropriate at normal reading (normal-speed reading in the positive direction), a sufficient contact is not obtained especially at the input end or the output end of a track during variable-speed reading. Therefore, the level of a read RF output is reduced and image data is not always obtained.
A trace error occurs against a target trace position due to factors such as bending of a recording track caused by a recording apparatus or a reading apparatus, trace distortion during reading, a recording-track positional shift caused by jitter in a speed servo during recording, and a movement-speed deviation caused by jitter in a phase-lock servo during reading. Therefore, image data is not obtained in some cases.
Image data for variable-speed reading is recorded into a tape serving as a recording medium, with a pattern (pattern corresponding to a reading speed assumed in advance) having a cyclic feature caused by a variable speed. A unit of interleaving is used for error-correcting outer codes. It is difficult during editing, such as connecting recorded images, to obtain an appropriate matching between two types of periodic features, image data for variable-speed reading and interleaving. To obtain matching, the scale of hardware increases and a software load also increases.